Direct mechanically-operated extrusion press

ABSTRACT

There is described an extrusion press (1) of a metal billet, comprising a die (3), a punch (2) able to push the billet through the die (3), and a container (4) of the billet upstream of the die (3). Said extrusion press (1) further comprises a screw (5) with which the punch (2) is integral, able to engage a nut screw (6) provided in the extrusion press (1). At least one electric motor (7) drives the reciprocal movement of the screw (5) and nut screw (6), thus causing the translation of the punch (2) in the extrusion direction.

BACKGROUND OF THE INVENTION

The present invention relates to a direct mechanically-operated extrusion press for metal materials, with a punch driven by a screw-nut screw system.

Extrusion presses able to produce extruded metal products typically comprise a punch able to press a metal billet in a die.

Said punch is integral with a cylinder, the translation of which occurs by pressurizing a hydraulic fluid.

The cylinder is a single-effect cylinder and consists of a piston and a sleeve. The introduction of pressurized fluid into the rear part of the sleeve causes the advancement of the piston and therefore of the punch, which presses the billet into the die.

The fluid is pressurized by hydraulic pumps and once introduced into the chamber of the sleeve, said pressure turns into force.

Disadvantageously, a hydraulic system causes a series of problems due to the complexity of the system, including the classical problems of all hydraulic machines, such as the leakage problem affecting the hydraulic fluid, the periodic replacement thereof, the recovery and disposal thereof, as well as the increased maintenance labor required to maintain the efficiency of a complex hydraulic system in which the assembly of valves, solenoid valves, fluid filters, air filters, pipes, proportional boards, etc. requires an increased maintenance expertise. Considering that the maximum pressure required to generate the extrusion force normally varies from 25 to 30 MPa, the hydraulic circuit is susceptible of stresses from continuous cycles induced by cyclical increases and decreases of the hydraulic pressure. Additionally, the problem of flammability of the fluid also exists, because the spontaneous combustion is triggered if it comes into contact with the hot metal (which generally is at 500° C.). In such a case, certain users may use delayed flammability fluid.

PRIOR ART

US-2015/0040635 describes a hybrid system which combines a hydraulic system like that described above, with an electric system with electric motors which operate pinions engaging racks which help the translation of the cylinder but which are not capable of generating all the force required to perform the plastic deformation of the metal, i.e. the extrusion. Given that this solution consists of a dual or hybrid system, it is doubly complex and in any case the problem of the circulation of the fluid, the cooling thereof, the filtering and periodic replacement thereof due to its deterioration remains, with all the associated and costly scheduled and corrective maintenance operations. In this solution, the main force generated for the extrusion is created by pumps which pressurize a hydraulic fluid.

WO-2016056276 shows an extrusion press electrically driven by drums about which cables are wound. A transverse head integral with the extrusion punch is moved by a pulley. Electric motors cause the winding/unwinding of the cables. The use of cables and large drums results in a significant volume, in addition to the wear to which said components are subjected. Moreover, given that the cables are susceptible of twisting and natural extension (elasticity of the metal) thereof, they do not allow a positioning accuracy under load which also may reach 50 MN of force. Moreover, the more the punch moves towards the die, the less the force resulting from this system, up to reaching zero. This is a limitation which is difficult to be overcome. This application is applicable only to presses having limited extrusion force due to the increased forces involved.

JP-201604337 also includes the use of drums and cables for pushing the punch. Said cables are fixed at one end to a body with which the cylinder supporting the punch is integral. Therefore, said cables feed the punch towards the die. As in the above-mentioned document, the Japanese patent also suggests the use of cables as pushing means, i.e. elements subjected to wear and which are cumbersome and with a push which is not very controllable.

It is worth noting that the force required for the extrusion per se (the force by which the plastic deformation of the billet occurs, namely the extrusion) is always generated, even in the hybrid systems described, by the pressurization of the fluid and never by the electric motors directly connected to the punch. The mechanically/electrically-operated part is designed to serve auxiliary functions only, never the main one, i.e. the force of extrusion.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an extrusion press in which the extrusion force is generated by mechanical means only, without the interposition of pressurized hydraulic means.

It is a further object of the present invention to ensure, by said mechanical means, at least the same push as the known systems, with less maintenance expenses and energy consumption.

It is a still further object for said mechanical means to be slightly or not subjected to wear so as to limit the unexpected production stops and the subsequent losses due to production stops.

Advantageously, the push of the punch is caused by one or more electric motors directly mechanically connected to the punch by a screw-nut screw system, without the aid of cylinders and/or hydraulic pistons which generate by themselves the extrusion force required.

The screw-nut screw extrusion system allows reduced energy costs.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become more apparent from the following detailed description of an exemplary practical embodiment thereof, shown by way of non-limitative example in the accompanying drawings, in which:

FIG. 1 shows a partially cross-sectional side view of an extrusion press according to the present invention;

FIG. 2 shows a sectional view according to line II-II in FIG. 1;

FIG. 3 shows a block of the sectional view in FIG. 2;

FIG. 4 shows a body of the sectional view in FIG. 2;

FIG. 5 shows a cylinder of the sectional view in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

An extrusion press 1 able to transform a metal billet profile by plastic deformation (extrusion) comprises a punch 2 able to push the billet through a die 3.

The billet is supported and guided by a container 4 which limits the expansion thereof during the push through the die and is placed between the punch and the die and guides the billet towards the die.

Punch 2 is integral with a screw 5 (see circle A in FIG. 1 in which the threading of screw 5 is depicted on enlarged scale).

Screw 5 engages a nut screw 6 which substantially is an annular-shaped body with an inner threaded surface.

Said nut screw 6 is driven to rotation about an axis E of screw 5 by one or more electric motors mechanically connected thereto. FIG. 1 depicts an annular-shaped electric motor 7 alone.

Said electric motor 7 comprises a rotor 71 integral with the nut screw 6 and a stator 72 integral with a base 8 by a block 9.

The nut screw 6 includes a cylindrical outer surface 64 able to slide on a cylindrical inner surface 91 of a cylindrical cavity 93 of block 9.

An interstice 94 is provided between said cylindrical outer surface 64 and said cylindrical inner surface 91, which is able to accommodate lubricating fluid to facilitate the sliding of body 6 in block 9.

Body 6 further comprises an annular portion 65 (FIG. 1) which abuts against block 9, like a portion of rotor 71, thus axially blocking the body 6.

The extrusion press 1 further comprises a shear 10 able to separate the non-extruded end portion of the billet (referred to as a discard) after the extrusion, such as described in International Patent Application WO-2017103828, for example.

A cylindrical bar 11 connects the container 4 of the billet with block 9. Such a connection is made by a screw and a nut screw and is electrically operated. The electrically driven screw-nut screw function aims at moving the billet container 4 along axis E.

Moreover, the extrusion press 1 preferably but not necessarily comprises a lubrication unit able to insert lubricating fluid between screw 5 and nut screw 6 in order to limit the friction and thus the energy expenditure of the electric motor 7.

With regard to the operation, motor 7 rotates the nut screw 6, which allows the translation of screw 5 along axis E due to the engagement thereof.

During the extrusion, the nut screw 6 rotates so as to cause the displacement of screw 5, and therefore of punch 2, towards the container 4 in which the billet is accommodated (to the right, looking at FIG. 1).

Once in contact with the billet, punch 2 pushes the billet through die 3, thus causing the plastic extruded deformation thereof, i.e. generating a profiled element.

Once the extrusion has been complete, motor 7 reverses the rotation of the nut screw 6, causing screw 5, and therefore punch 2, to retract, thus returning to a configuration like that depicted in FIG. 1.

Advantageously, the push of punch 2 is caused by an electric motor which directly converts the driving torque thereof into axial force by screw-nut screw motion transmission means without the aid of hydraulic means, i.e. the possible pressurization of hydraulic means does not generate any force which contributes to the required extrusion force.

Preferably, there are between 40 and 60, even more preferably 50 threads engaged in the engagement of screw 5 and nut screw 6.

Preferably, the surface engaged in said engagement is between 1 m² and 1.5 m², even more preferably about 1.38 m².

The aforesaid sizes cause a specific load ranging between 1 and 1.5 kg per square millimeter, preferably of 1.3 kg per square millimeter.

The maximum feeding speed of cylinder 5 preferably is between 25 and 35 mm/second, preferably 30 mm/second, with a rotation speed preferably being between 25 and 35 revolutions per minute, preferably 27 revolutions per minute corresponding to 0.45 revolutions per second.

The return speed of the cylinder obviously is greater (without a load), preferably between 550 and 650 mm/second, preferably 600 mm/second, with a rotation speed preferably between 800 and 1000 revolutions per minute, preferably 900 revolutions per minute corresponding to 15 revolutions per second.

Alternatively, instead of motor 7, there may be a toothed crown on which two or more planetary motors are engaged, the purpose of which is the rotation of the aforesaid crown directly fixed to the nut screw 6.

Advantageously, the screw-nut screw extrusion system allows a reduced volume of the press, increased cleaning, lower maintenance costs and reduced energy costs.

The push generated by this mechanical system is sufficient for the extrusion of any metal material without the interposition of a compressed fluid and of the complex hydraulic circuits required therein.

Alternatively, it may be provided that the nut screw 6 translates along axis E with the punch 2 integral therewith, and the screw 5 rotates, thus feeding and pushing the punch forwards, with which it is integral.

The same above-described screw-nut screw pushing system is also applicable with horizontal screws (e.g. four in number), with which respective nut screws are engaged, which move a vertical plate with which the punch is integral, along axis E. This includes the possibility for the nut screws to rotate-translate on the screws, or alternatively for the screws to rotate in order to feed the nut screws which are integral with the vertical plate. 

1. An extrusion press of a metal billet, comprising a die, a punch able to push the billet through the die and a container of the billet upstream of the die, wherein a screw which the punch is integral to, able to engage with a nut screw in the extrusion press, at least one electric motor driving reciprocal movement of the screw and of the nut screw thus causing the movement of the punch in the extrusion direction.
 2. The extrusion press according to claim 1, wherein the nut screw is driven to rotate about an axis of the screw, corresponding to the movement direction of the screw, by said at least one electric motor.
 3. The extrusion press according to claim 1, wherein the nut screw is fixed and the screw is driven to rotate about an axis of the screw, corresponding to the movement direction of the screw, at least by said at least one electric motor.
 4. The extrusion press according to claim 1, wherein a plurality of horizontal screws which respective nut screws engage with, thus causing the movement in the extrusion direction of a vertical plate which the punch is integral to.
 5. The extrusion press according to claim 1, wherein there is a lubrication unit able to insert lubricating fluid between the screw and the nut screw.
 6. The extrusion press according to claim 1, wherein said at least one electric motor comprises a rotor integral with the nut screw, and a stator integral with a base.
 7. The extrusion press according to claim 1, wherein said at least one electric motor comprises planetary motors able to engage with a crown integral to the nut screw.
 8. The extrusion press according to claim 1, wherein a block which provides a cylindrical inner surface of a cylindrical cavity on which a cylindrical outer surface of the nut screw slides.
 9. The extrusion press according to claim 8, wherein an interstice is provided between said cylindrical outer surface and said cylindrical inner surface, able to accommodate lubricating fluid to facilitate the sliding of the nut screw in the block. 